The present invention relates to a method of manufacturing a fiber-reinforced thermoplastic resin of cellular structure. More particularly, the present invention relates to a method of manufacturing a lightweight, high strength construction material made of fiber-reinforced thermoplastic resin of cellular structure and having a specific gravity within the range of 0.2 to 1.0 and other physical properties comparable with those of a natural wood of a kind generally employed as a construction material.
The Japanese Patent Publication No. 48-8468, first published for opposition on Mar. 14, 1973, discloses a fiber-reinforced thermoplastic plate manufactured by applying a thermoplastic resin powder to glass fibers, while the latter are heated to a temperature higher than the softening point of the thermoplastic resin powder, so as to form resin-impregnated glass fibers and then applying a pressure to a mass of the resin-impregnated glass fibers, while the latter are heated to a temperature higher than the fluidizing temperature at which the thermoplastic resin starts its fluidization, to thereby provide the fiber-reinforced thermoplastic plate.
The Japanese Patent Laid-open Publication No. 48-40864, laid open to public inspection on June 15, 1973, discloses a fiber-reinforced thermosetting resin of cellular structure manufactured by applying a solution of expandable thermosetting resin to a plurality of rovings of glass fibers, collecting the resin-impregnated rovings to provide a substantially square-sectioned bundle of the rovings by the use of a bundling mold, applying a pressure to the bundle of the rovings during the passage thereof through the bundling mold to allow the thermosetting resin to be expanded and subsequently cured, and drawing the resultant fiber-reinforced thermosetting resin of cellular structure out of the bundling mold.
In the method of the Japanese Patent Laid-open Publication No. 48-40864, the thermosetting resin is an unsaturated polyester or urethane resin and, since this thermosetting resin even though applied in the liquid form tends to be readily expanded and cured in a relatively short period of time, for example, within 1 to 2 minutes, the thermosetting resin solution does not sufficiently penetrate into interstices of glass fibers making up the individual rovings. The consequence is that the resultant product is not sufficiently reinforced even though mixed with glass fibers.
The Japanese Patent Publication No. 49-31741, first published for opposition on Aug. 24, 1974, discloses a fiber-reinforced thermoplastic resin manufactured by immersing a fiber glass mat in a bath containing an emulsion of thermoplastic resin and then drying the emulsion-impregnated glass mat under heated condition, for example, at 130.degree. C., for a predetermined period of time, for example, 10 minutes. The fiber-reinforced thermoplastic resin according to this Japanese Patent Publication No. 49-31741 has failed to have a cellular structure and, therefore, cannot be used in such an application in which a wooden construction material is employed.
On the other hand, it is generally recognized that the thermoplastic resin, even when reinforced by glass fibers, cannot be improved so much as the thermosetting resin reinforced by glass fibers because most physical properties of the former are inferior to those of the latter. Moreover, although a method for impregnating glass fibers with an emulsion of thermoplastic resin is well known, no method has been found to manufacture a light-weight construction material, similar to the natural wood, by the employment of a blowing agent in the emulsion and this fact illustrates that the mere employment of the thermoplastic resin emulsion does not result in expansion of the thermoplastic resin.